The word stretchiest is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 16
Highest Scoring Words With Friends™ Plays In The Letters stretchiest
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Seven Letter Word Alert: (29 words)
cerises, cithers, cresset, etchers, etheric, heiress, heretic, hessite, hitters, recites, resects, retches, retests, richest, secrets, setters, sitters, streets, stretch, techies, tersest, testers, testier, tethers, theists, thirsts, tithers, titters, trisect